Condensate polishers are used to purify water in a large variety of systems. Condensate polishers are used chiefly in power plants or other plants condensing steam. Typical condensate polishers are designed for high flow and are composed of mixtures of cation and anion resins. As water flows over the ion exchange resin, charged particles (ions) in the water are drawn out and bonded to it. Two standard types of condensate polishers are deep bed polishers and powdered resin polishers.
Deep bed polishers comprise resin beads, approximately 500-1000 micro meters in diameter, contained in a column through which feed water is passed. The ratio of cation to anions beads may be varied depending on the expected concentration of ions in the water. In practice, many are heavy in cation bead concentration due to the large amount of cations, such as ammonia, that are added to the feed water in pre-filtering steps. An advantage of deep bed polishers is that they have large capacity and are relatively inexpensive to keep up. Unfortunately, when the beads have reached operational capacity in adsorbing ions, the process for regenerating the beads is onerous. This is primarily due to the difficulty in separating the anion from the cation beads. When the beads are being regenerated, they first need to be separated and separation needs to be substantially complete. A single anion bead, for example, can contaminate a large number of cation beads if it is not properly separated during the regenerating process. Deep bed polishers last for days or weeks depending on the nature of the feed water.
FIG. 1 shows an example of a deep bed polisher. Feed water 2 enters a deep bed polisher 4 and passes over a large amount of ion beads 6. A screen 8 prevents the beads from exiting the polisher with the filtered water 10.
Techniques for separating the ion exchange beads are varied and include suspending the beads in a neutral buoyancy solution so that the minute density difference between the cation and anion beads will allow the two to separate. Despite the ingenuity in the various techniques for separating the beads, the process is still problematic and time consuming.
The second type of common condensate polisher is the powdered resin system. In this technique the resin is reduced to powdered resin particles, of approximately 25 micrometers in size. The powdered resin is coated on a mesh large enough to allow water flow but fine enough to prevent passage of the powdered resin. Similar to the deep bed polishers, the concentration of anion powdered resin to cation powdered resin may be adjusted depending on expected need. Due to the powdered nature of the resin, these types of polishers are also good at filtering suspended impurities, such as iron oxide and sand. However, they are less effective at capturing ions than the deep bed polishers. Also, when the powdered resin reaches ion absorption capacity, the resin cannot be effectively regenerated and is disposed of and replaced.
FIG. 2 illustrates an example of a powdered resin polisher. Feed water 2 enters the powdered resin polisher 12 and passes over the powdered resin 13 that is mounted on a mesh 14. The filtered water then is drawn from the polisher 10. Powdered resin polishers typically last for hours or days depending on the nature of the feed water.
What is needed is a condensate polisher that is easy to regenerate, has excellent ion exchange efficiency and filters suspended particles.